Relatively recently, implantable prosthetic devices in the nature of infusate pumps have been developed for dispensing infusates such as insulin at a very low flow rate to a selected location in the human body over the long term. Eventually the fluid reservoir in such a device empties so that, if the device is to continue performing its function, its reservior must be refilled with a fresh supply of infusate. To avoid having to operate on a patient to remove the implanted device each time it is necessary to refill it, the device is designed with a penetrable self-sealing septum in a wall of the device which normally seals a passage leading to the device's reservoir.
With the pump or other device implanted in the patient's body so that the septum underlies the skin, its reservoir can be refilled, as needed, simply by injecting a fresh supply of infusate by means of a hypodermic needle through the patient's skin, through the septum and into the infusate reservoir or chamber inside the device. In some cases, the act of refilling the device also recharges its power supply so that the unit can operate uninterruptedly for a prolonged period. Implantable pumps of this general type are disclosed, for example, in U.S. Pat. No. 3,731,681 and 3,951,147.
Other rechargeable, battery-operated implantable devices such as pumps and pacemakers have septums through which needle-like electrical terminals are injected to make contact with terminals inside the devices leading to the battery.
In some cases, it has proven difficult to locate the septum of the implanted device in order to inject a needle into it to refill or recharge the device. One reason for this difficulty is that the physical movements of the patient after the device is implanted sometimes cause the device to shift its position within the body so that its septum is no longer at its original location. Thus a physician cannot rely on a datum such as a tatoo marked on the patient's body to pinpoint the septum after the device is implanted.
It should be mentioned at this point also that the implanted device may not only shift laterally relative to its original position, but also it may cock or tilt so that its septum is skewed relative to the overlying surface of the patient's body. Thus, even if the device's septum underlies the original datum, when the hypodermic is inserted through the patient's skin, it may pierce the septum at a considerable angle so that the needle does not seat properly at the charging station of the device. Also, in a worst case situation, the needle point may strike a hard surface inside the implanted device and be broken.
The septum locating problem is particularly acute in the case of very heavy or obese people because the implanted device underlies several layers of fatty tissue and is more apt to shift its position within the body.
Until now, there has been no easy way to precisely pinpoint the location of the septum of such an implanted device except for repeated injections on a trial and error basis. This procedure is not only painful to the patient, but also it opens the possibility of the infusing hypodermic needle missing the septum entirely unbeknownst to the physician. In that event, a relatively large quantity of infusate could be injected locally into the patient all at once with possibly harmful results. Also as alluded to previously, unless the needle is aimed properly, it could strike a hard surface of the device and break within the patient's body with equally distressing results.